You can get cheap s/h components (OEM and “Component” (e.g. Wishon, Geek)) from USA via forums – I can give you links. Only issue is convincing sellers to send over here.
It’s actually worthwhile buying new from there too if you need supplies like shafts, grips, ferrules epoxy etc. ‘Cos by the time you buy all of them separately via ebay, with all of the individual P&P’s.....
Be sure to specify USPS rather than UPS – less risk to get picked out by customs for duty.
My favourite site is GolfWorks ‘cos they sell the great range of Maltby heads. Solid well designed stuff.
“Component” stuff tends to fall into categories – A-list stuff like Wishon, Nakashima,Infiniti etc, B-list like Maltby, Acer (via Hireko), and thenthere's C-list...
For feedback and reviews on high end try the USA forums, for reviews of B& C list try golfreview.com.
By the by: I have an Adams BUL5000 (the current model) head for sale. 10.5deg, vgc, no headcover. Would be £65 incl a ferrule and the P&P to UK.